1. Field of the Invention
The present invention relates generally to catheters inserted into the vascular system for extended periods of time, and more particularly, to a collapsible catheter for insertion into a blood vessel, and methods for placing such collapsible catheter into the blood vessel.
2. Description of the Related Art
Insertion of catheters into the vascular system of humans and animals is a commonly performed procedure. These catheters function as a conduit for infusion of fluids or drugs. When a catheter needs to be in place for greater than three or four days, it is common to place a so-called central line catheter, and to locate the leading tip of the catheter in one of the major veins at the top of the chest leading to the heart, such as the subclavian vein or the major veins of the mediastinum. In some instances, but less commonly, catheters are passed from the lower half of the body into the inferior vena cava. Central catheters are usually passed into the subclavian vein, jugular vein, or into an antecubital vein at the elbow. Such central catheters may have single or multiple lumens, and are typically made from a relatively rigid plastic material with a standard, round cross-section, both to facilitate placement of the catheter into the vein and to prevent the catheter lumens from collapsing within the vein. Generally speaking, these catheters are constructed in such a way that the lumen or lumens extending therethrough retain their cross-sectional configuration unless an external mechanical force compresses the catheter.
A complication of placing a central line catheter is the formation of clots on the wall of the catheter located in the vascular system. Blood clots form for several reasons. The presence of any object occupying space within a blood vessel causes turbulence and slowing of the blood flow through the vessel, and these factors induce the formation of clots. Generally, the greater the cross-sectional area of the catheter relative to the blood vessel, the greater the induced turbulence and slowing of the blood. In addition, the catheter is a foreign body, and the surface of the catheter in contact with blood acts as a nidus for clot formation. Once again, the greater the amount of surface area of the catheter or other foreign body in contact with the blood, the more likely that clots will form.
Such clots can break away and flow in the blood stream to the heart and lungs, causing severe complications. Furthermore, the formation of clots can often cause such veins to become irreversibly damaged and thrombose, preventing further blood flow through such veins. This may ultimately cause debilitating swelling of the limb being drained by these veins.
Apart from the risks of forming clots within the blood vessel, present central line catheters also suffer from susceptibility to clotting within the catheter itself. In this regard, blood enters the lumen of the catheter and forms a clot within the lumen, obstructing the passage of fluids through the catheter into the vein, and thereby rendering it unusable. While such clots may not be life threatening to the patient, blockage of the catheter can require removal and replacement of the catheter, a procedure which poses an inconvenience to both the patient and the attending physician, and adds to the cost of maintaining venous access.
U.S. Pat. No. 5,176,659 issued to Mancini discloses an expandable intravenous catheter which has a lesser diameter during insertion into a vein, and which is thereafter expanded following placement to a larger diameter. While such device simplifies insertion of the catheter, it still maintains a sizable obstruction within the vein with a significant exposed surface area, and it still permits blood to enter the lumen of the catheter in the absence of fluid flow.
U.S. Pat. No. 5,106,368 to Uldall et al. discloses a dual lumen catheter for vascular access. The distal portion of the catheter includes two tubular members attached to each other, only one of which is collapsible. The catheter is inserted into a blood vessel through a peel-away sheath, and over both a stiffening cannula and a guide wire. The collapsible lumen returns to its original circular shape once placed in the blood vessel. Thus, no reduction of the cross-sectional area, or surface area, of the catheter is achieved after the catheter is placed. In addition, blood can still enter both lumens of the catheter in the absence of fluid flow.
U.S. Pat. No. 4,406,656 issued to Hattler et al. discloses a multi-lumen catheter adapted to be inserted through the center of an insertion needle into the vein of a patient. The catheter disclosed by Hattler et al. includes two or more collapsible lumens formed around a flexible, but non-collapsible, central lumen. The collapsible lumens expand outwardly under the pressure of fluid flow and collapse to a smaller cross-sectional area in the absence of fluid flow. However, the central lumen of the Hattler et al. device is formed of materials which retain the shape of the central passageway whether or not fluids flow therethrough. Thus, even when the collapsible lumens are collapsed, the device disclosed by Hattler et al. still approximates the cross-sectional area of a conventional single lumen catheter. Indeed, Hattler et al. state that the central lumen of the disclosed multi-lumen catheter requires a certain degree of stiffness or rigidity to provide sufficient structural support so that the catheter can be handled as are conventional catheters. While the device disclosed by Hattler et al. somewhat reduces the cross-sectional area of a multi-lumen catheter, it does not reduce the cross-sectional area or surface area of the catheter below that of a conventional single lumen catheter, nor does it prevent blood from entering the central, non-collapsible lumen in the absence of fluid flow.
Accordingly, it is an object of the present invention to provide a central line catheter which reduces the likelihood of the formation of clots within the blood vessel into which the catheter is placed.
It is another object of the present invention to provide such a catheter which presents a minimal cross-section obstruction to the normal flow of blood within the blood vessel when the catheter is not being used for infusion, while providing a satisfactory flow path to infused fluids during infusion procedures.
It is still another object of the present invention to provide such a catheter which minimizes the surface area of the catheter exposed to the blood when infusion procedures are not being performed.
It is a further object of the present invention to provide such a catheter which minimizes the likelihood of blood entering the lumen of the catheter and forming a blockage therein.
A still further object of the-present invention is to provide a method for conveniently placing such a catheter within the desired blood vessel using commonly available vascular apparatus.
These and other objects of the present invention will become more apparent to those skilled in the art as the description of the present invention proceeds.